Fix exercise extra_fields migration for non-m_of_n mastery models (#5714)

* Fix migrate_extra_fields to null m/n for non-m_of_n mastery models

Old-style exercise extra_fields were being migrated with non-null m/n
values for non-m_of_n mastery models (e.g. do_all, num_correct_in_a_row).
The mastery criteria JSON schema requires m and n to be null for these
models, causing frontend AJV validation to fail and exercises to appear
incomplete.

- Fix migrate_extra_fields to set m/n to null for non-m_of_n models
- Add management command fix_exercise_extra_fields to repair existing
  data in production

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* Migrate old-style exercise extra_fields on ricecooker import

The ricecooker import path (create_node) was writing old-style
extra_fields directly to the DB without running migration. This
ensures incoming exercise data is migrated to the new-style
options.completion_criteria format before being persisted.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* Cleanup management command and add more logging.

* Target dry_run more focally for better info, cleanup redundant save.

* Lazy loading, lazy coding.

* Mark_complete returns an empty list if complete.

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

Author: rtibbles

contentcuration/contentcuration/management/commands/fix_exercise_extra_fields.py

@@ -0,0 +1,140 @@
+import json
+import logging as logmodule
+import time
+
+from django.core.management.base import BaseCommand
+from le_utils.constants import content_kinds
+from le_utils.constants import exercises
+
+from contentcuration.models import ContentNode
+from contentcuration.utils.nodes import migrate_extra_fields
+
+logging = logmodule.getLogger("command")
+
+CHUNKSIZE = 5000
+
+
+def _needs_m_n_fix(extra_fields):
+    """
+    Check if already-migrated extra_fields have non-null m/n
+    on a non-m_of_n mastery model.
+    """
+    try:
+        threshold = extra_fields["options"]["completion_criteria"]["threshold"]
+    except (KeyError, TypeError):
+        return False
+    mastery_model = threshold.get("mastery_model")
+    if mastery_model is None or mastery_model == exercises.M_OF_N:
+        return False
+    return threshold.get("m") is not None or threshold.get("n") is not None
+
+
+def _needs_old_style_migration(extra_fields):
+    """
+    Check if extra_fields still has old-style top-level mastery_model.
+    """
+    return isinstance(extra_fields, dict) and "mastery_model" in extra_fields
+
+
+class Command(BaseCommand):
+    help = (
+        "Fix exercise extra_fields that were migrated with invalid m/n values "
+        "in their completion criteria threshold. Non-m_of_n mastery models "
+        "require m and n to be null, but old data may have had non-null values "
+        "that were carried over during migration. Also migrates any remaining "
+        "old-style extra_fields to the new format."
+    )
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            "--dry-run",
+            action="store_true",
+            help="Report what would be changed without modifying the database.",
+        )
+
+    def handle(self, *args, **options):
+        dry_run = options.get("dry_run", False)
+        start = time.time()
+
+        # Single pass over all exercises, filtering in Python to avoid
+        # expensive nested JSON field queries in the database.
+        queryset = ContentNode.objects.filter(kind_id=content_kinds.EXERCISE)
+
+        total = ContentNode.objects.filter(kind_id="exercise").count()
+        migrated_fixed = 0
+        migrated_complete = 0
+        old_style_fixed = 0
+        old_style_complete = 0
+        exercises_checked = 0
+
+        for node in queryset.iterator(chunk_size=CHUNKSIZE):
+            fix_type, complete = self._process_node(node, dry_run)
+            if fix_type == "old_style":
+                old_style_fixed += 1
+                if complete:
+                    old_style_complete += 1
+            elif fix_type == "m_n_fix":
+                migrated_fixed += 1
+                if complete:
+                    migrated_complete += 1
+            exercises_checked += 1
+            if exercises_checked % CHUNKSIZE == 0:
+                logging.info(
+                    "{} / {} exercises checked".format(exercises_checked, total)
+                )
+                logging.info(
+                    "{} marked complete out of {} old style fixed".format(
+                        old_style_complete, old_style_fixed
+                    )
+                )
+                logging.info(
+                    "{} marked complete out of {} migrated fixed".format(
+                        migrated_complete, migrated_fixed
+                    )
+                )
+
+        logging.info("{} / {} exercises checked".format(exercises_checked, total))
+        logging.info(
+            "{} marked complete out of {} old style fixed".format(
+                old_style_complete, old_style_fixed
+            )
+        )
+        logging.info(
+            "{} marked complete out of {} migrated fixed".format(
+                migrated_complete, migrated_fixed
+            )
+        )
+        logging.info(
+            "Done in {:.1f}s. Fixed {} migrated exercises, "
+            "migrated {} old-style exercises.{}".format(
+                time.time() - start,
+                migrated_fixed,
+                old_style_fixed,
+                " (dry run)" if dry_run else "",
+            )
+        )
+
+    def _process_node(self, node, dry_run):
+        ef = node.extra_fields
+        if isinstance(ef, str):
+            try:
+                ef = json.loads(ef)
+            except (json.JSONDecodeError, ValueError):
+                return None, None
+        if not isinstance(ef, dict):
+            return None, None
+
+        if _needs_old_style_migration(ef):
+            ef = migrate_extra_fields(ef)
+            fix_type = "old_style"
+        elif _needs_m_n_fix(ef):
+            ef["options"]["completion_criteria"]["threshold"]["m"] = None
+            ef["options"]["completion_criteria"]["threshold"]["n"] = None
+            fix_type = "m_n_fix"
+        else:
+            return None, None
+        node.extra_fields = ef
+        complete = not node.mark_complete()
+        if not dry_run:
+            node.save(update_fields=["extra_fields", "complete"])
+        return fix_type, complete